Overlord, Shockwave and Straxus [not in the same movie though, I'd be happy seeing them across a trilogy].
There are so many Decepticons that could rule the Decepticons now. Galvatron via resurrected Megatron from Unicron, Overlord, Thunderwing, and even Bludgeon.
Shockwave is dead when they kill someone they kill someone. Although I perfer these Straxus: Richard McGonagle Thunderwing: Micahel T. Wiess Cyclonus: John DiMaggio Thundercracker: Wade Williams Skywarp: Larry Cedar Galvatron: Hugo Weaving Unicron: Clancy Brown
Straxus as leader, Jhiaxus as his top scientist/second in command, maybe throw Thunderwing in there somewhere (maybe as a weapon?), introduce the urban terrorist "Wildrider", throw in a little Motormaster muscle to stand against Optimus, have Ratbat or Obsidian be the new intelligence guy.